1. Field of the Invention
The present invention relates to bearing structures such as those used in fan motor assemblies, and particularly to a bearing structure which comprises a first member and a second member where a material of the first member is different from a material of the second member.
2. Description of Prior Art
Sliding bearings are widely used in fan motor bearing assemblies mainly because of their low cost. A sliding bearing is mostly made of metallic sintered material or ceramic sintered material. A typical metallic bearing has many open pores on its surface suitable for holding lubricating oil therein. Therefore the metallic bearing can provide good lubrication. However, the metallic bearing is prone to wear out after continued use. FIG. 4 illustrates a conventional metallic bearing accommodating a shaft therein. FIGS. 5A and 5B illustrate typical situations when the shaft rotates at high speed in the bearing. The shaft deviates from a central axis of rotation, and contacts the bearing. Thus the bearing is easily worn out, and a lifespan of the bearing is reduced. In contrast, a typical ceramic bearing is highly resistant to friction wear. Nevertheless, a surface of the ceramic bearing has poor capability for holding lubricating oil therein. When the ceramic bearing operates with only a little lubrication, it is also easily worn out. In addition, increased friction during operation results in increased vibration.
U.S. Pat. No. 5,997,265 discloses an improved bearing structure. An annular groove is defined in an inner surface of a bearing of the bearing structure. The groove gives the bearing increased oil holding capacity, reduces friction between a shaft and the bearing, and extends a lifespan of the bearing structure. U.S. Pat. No. 5,927,859 discloses a bearing structure defining a through hole, a cavity and a plurality of slots in communication with the cavity. A shaft disposed in the through hole forms two sets of threads that spiral in opposite directions. When the shaft rotates, grease is forced along the threads such that it circulates through the cavity, the slots and the through hole. However, both the above-disclosed bearing structures require extra structures to be added to the bearing. Manufacturing of the bearing is more complicated, and costs of the bearing structure are increased.
Thus, an improved bearing structure which overcomes the above-mentioned problems is desired.